Network nodes, such as e.g. User Equipment (UE), also known as mobile stations, wireless terminals and/or mobile terminals are enabled to communicate wirelessly in a wireless communication system, sometimes also referred to as a cellular radio system. The communication may be made e.g. between two user equipment units, between a user equipment and a regular telephone and/or between a user equipment and a server via a Radio Access Network (RAN) and possibly one or more core networks.
The user equipment units may further be referred to as mobile telephones, cellular telephones, e-readers, laptops with wireless capability etc. The user equipment units in the present context may be, for example, portable mobile devices, enabled to communicate voice and/or data wirelessly, via the radio access network, with another entity, such as a network node.
However, the network nodes herein discussed may comprise a base station e.g. a Radio Base Station (RBS), which in some networks may be referred to as “eNB”, “eNodeB”, “NodeB” or “B node”, depending on the technology and terminology used. The network nodes may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the network node/base station at a base station site. One base station, situated on the base station site, may serve one or several cells. The network nodes communicate over the air interface operating on radio frequencies with the user equipment units within range of the respective network node.
In some radio access networks, several network nodes may be connected, e.g. by landlines or microwave, to a Radio Network Controller (RNC) e.g. in Universal Mobile Telecommunications System (UMTS). The RNC, also sometimes termed a Base Station Controller (BSC) e.g. in GSM, may supervise and coordinate various activities of the plural network nodes connected thereto. GSM is an abbreviation for Global System for Mobile Communications (originally: Groupe Spécial Mobile).
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), network nodes, or base stations, which may be referred to as enhanced Node Bs, eNodeBs or eNBs, may be connected via a gateway e.g. a radio access gateway, to one or more core networks.
The 3GPP is responsible for the standardization of LTE. LTE is a technology for realizing high-speed packet-based communication that may reach high data rates both in the downlink and in the uplink, and is thought of as a next generation mobile communication system relative UMTS.
Some embodiments discussed herein may fall into the area of Admission Control and Quality of Service (QoS) in particular for Time-Division Duplex (TDD) in LTE. TDD is an application of time-division multiplexing to separate uplink and downlink signals in time, possibly with a guard period situated in the time domain between the uplink and downlink signalling.
However, embodiments of the wireless communication system described herein may be configured to operate according to the Frequency Division Duplex (FDD) principle, according to different embodiments.
FDD means that the transmitter and receiver operate at different carrier frequencies. The subsequently described explanations and embodiments are exemplified in an FDD LTE environment, as a non-limiting example. However the methods and apparatuses may easily be generalized and applied to e.g. a TDD LTE system, and also to cellular systems other than based on the LTE standard, or in fact any other cell based access technology where in-band relaying may be applied.
The task of Admission Control is to admit or reject resource requests. In mobile radio communication systems, these establishment requests are made for new radio bearers. Admission control considers the overall resource situation, e.g. in the network nodes and infrastructure comprising both radio access network and core network, the Quality of Service (QoS) requirements, the priority levels and the provided QoS of in-progress sessions and the QoS requirement of the new radio bearer request.
In LTE air interface resources like Resource Blocks (RBs) for Physical Downlink Shared Channel/Physical Uplink Shared Channel (PDSCH/PUSCH) and Control Channel Elements (CCEs) are allocated to Evolved-Radio Access Bearers (E-RABs), or radio access bearers as they also may be referred to as. A prioritisation scheme may be used by the scheduler to make sure resources are assigned to E-RABs in accordance to their QoS requirements on sub-frame basis.
Of particular interest may be the situation when the resources comprising control channel elements are associated with Physical Downlink Control Channel (PDCCH) in TDD LTE.
A scheduler comprised within a network node, or eNodeB may try to assign resources to the QoS E-RABs to fulfil their QoS requirements. Whenever the scheduler is congested, it assigns resources such that the QoS requirements are fulfilled in the order indicated by the priority of the QoS E-RABs. There may be two aspects related to this way of prioritising with respect to QoS requirements.
Firstly, some E-RABs do not have any QoS requirements at all, so-called best-effort or non-Guaranteed Bit Rate (non-GBR) bearers. This means that scheduling may not consider those E-RABs in congested scenarios. Then there is a risk that this class of E-RABs is starved out since only E-RABs with specified QoS requirements are scheduled.
Secondly, if too many E-RABs with QoS requirements are admitted scheduling will at some point fail to provide resources to all of them. Users may have been admitted at a point in time when radio conditions and mobility were favourable in the sense that QoS could be provided. But due to increasing mobility and worsened radio conditions the resources may at a later point in time not be enough to provide QoS for the admitted E-RABs.
Those two aspects may be dealt with by an Admission Control function that monitors the resources handled by the scheduler. These resources are typically control channel elements of the PDCCH and resource blocks of PDSCH/PUSCH. Admission Control strives for having the load due to E-RABs with QoS requirements below a QoS threshold expressed as a percentage of the maximum amount of the resource. It does so by rejecting initial access whenever load due to E-RABs with QoS requirements is above the QoS threshold. The QoS threshold could for instance relate to the contribution from all the Guaranteed Bitrate Bearers (GBRs).
This kind of Admission Control may then assist in protecting E-RABs without any QoS requirements. It also allows for statistical fluctuations with regard to the air interface resources, since the load for high-priority traffic may be limited to a value lower than the maximum level of the resource. Then integrity of the QoS E-RABs may be protected with some level of probability since resources above the threshold are available for the high-prioritized traffic in congested scenarios. Tuning the threshold makes possible to adjust that probability. Tuning the margin between the threshold and the maximum level of the resource is of special interest when the high-prioritized traffic consists of GBR traffic where service blocking is desired rather than service dropping.
In FIG. 1A are the loads on different resources handled by scheduling in a FDD case illustrated. Whenever load on a resource exceeds its threshold, Admission Control rejects any E-RAB request with an associated QoS requirement.
The load is separately measured for each resource. This means one load measure for resource blocks utilization on PDSCH and PUSCH respectively. Moreover, since PDCCH is a common resource for both downlink (DL) and uplink (UL) in the sense that it transmits assignments for both PDSCH and PUSCH, control channel element utilisation on PDCCH are treated as one resource.
In the present context, the expressions downlink, downstream link or forward link may be used for the transmission path from the network node to the user equipment. The expression uplink, upstream link or reverse link may be used for the transmission path in the opposite direction i.e. from the user equipment to the network node.
In this disclosure the focus is on the control channel element resource in the case of TDD in LTE. It is however possible to generalise the method to any time division duplex wireless technology with a downlink control channel similar to PDCCH.
In FIG. 1A and FIG. 1B, the load on different resources measured in percentage of maximum capacity for each specific resource is illustrated. The maximum limits for the various resources vary, but a QoS Admission threshold is configured as a percentage of the maximum limit.
For FDD, the PDCCH is a resource common to downlink and uplink since it is always, in every subframe, possible to transmit in both links. Then scheduling lets both downlink (requesting assignments) and uplink (requesting grants) to compete for these resources. The competition is based on a prioritization scheme where the priority of the user equipment is based on its E-RABs and their QoS requirements. An admission control function can then monitor the control channel element resource load due to E-RABs with QoS requirements as a resource common downlink and uplink.
This situation is however completely different for TDD. Firstly, simultaneous uplink and downlink transmission is not allowed. What subframes are for downlink and what subframes are for uplink is determined from the specific uplink-downlink configuration.
Second, PDCCH sent in a specific subframe always carry assignments for downlink transmission, but only for a subset of these subframes there are control channel elements carrying grants for uplink transmission.
To represent the control channel element utilisation in TDD LTE as one resource without considering there are different types of subframes with respect to whether downlink only or downlink/uplink combined are competing for PDCCH resources would be similar to combining the resource block utilisation of PDSCH and PUSCH (for downlink and uplink) as one resource. That way the Admission Control function would be out of touch as to how the different links are loading the scheduler, with regard to E-RABs with QoS requirements.